1. Field of the Invention
The present invention relates to a method for reducing power consumption of a battery of a mobile terminal, and more particularly to a method for managing extended neighbor cells of a mobile terminal designed to save power of a battery as well as search time at a visited location.
2. Description of the Related Art
According to the GSM (Global System for Mobile communication) specification, each mobile terminal performs cell management using information on BCCH (broadcast control channel) allocation lists (hereinafter, called “BA lists”), which are included in system information 2 (2bis and 2ter) received in an idle mode by the mobile terminal and system information 5 (5bis and 5ter) received in a dedicated mode by the mobile terminal, both of which belong to various system information relayed through BCCHs in an RPLMN (registered public land mobile network) to which a serving cell belongs. The serving cell is that cell to which the mobile terminal is currently assigned. Each BCCH, as a channel for transmitting various system parameters, transmits various information on a frequency, such as an operator, an identifier, cell location, or cell location variation.
The system information 2 is a neighbor cell description which is used in an idle mode of the mobile terminal. The neighbor cell description represents BCCH frequencies used in the cells neighboring a serving cell that the mobile terminal is assigned to. For this reason, the neighbor cell description is called the BA list.
The conventional cell management is divided into information collection for performing cell reselection in the idle mode of the mobile terminal, and neighbor cell management for performing hand-over in the dedicated mode of the mobile terminal. This neighbor cell management becomes still more important, as a general packet radio service (hereinafter, referred to as “GPRS”) is introduced. Thus, reselection by the network has been introduced, as well as automatic cell reselection by the mobile terminal.
According to the GSM specification, variation from the present GSM to a third generation GSM (3GSM) allows less complicated conditions that the mobile terminal can determine a home PLMN (HPLMN) when within a visited PLMN (VPLMN).
The time for rescanning the HPLMN may be previously stored at a subscriber interface module (SIM) or newly provided by an over-the-air technique, in which the time has an interval of 6 minutes and a basic value of 30 minutes, which is also gradually reduced to the minimum value of 6 minutes. There are increasing service providers, who make use of 6 minutes as the basic value.
To rescan the HPLMN, a mobile terminal must measure the electronic power of the frequencies received from its vicinities and find the frequency satisfying the conditions required by the GSM 03.22 specification. In this case, to search and find frequencies for either the HPLMN or SIM preferred PLMN with respect to new frequencies of a varying field requires great amounts of battery power, as well as considerable amounts of time.
Considering that different common carriers do not share a frequency band with each other within the same area, there is a problem in that attempts for frequent measurement of electric power and for the resulting synchronization of many frequencies brings about unnecessary consumption of battery power. For instance, at their worst, there is a possibility to be in the face of a circumstance in which electric power of peripheral frequencies must be measured at an interval of 6 minutes.